1. Field of the Invention
The invention relates to a fan control device and a fan control method.
2. Related Art
Fans are installed in various types of electrical devices to facilitate the heat dissipation in these devices by adjusting the rotation speed of the fan using a proper fan control device.
Referring to FIG. 1A, a conventional fan control device includes an impeller sensor 11, a driving chip 12 and a digital-to-analog converter 13. The impeller sensor 11 measures a position of an impeller of a fan 14 and generates a measurement value 111 according to the position of the impeller. The driving chip 12 receives the measurement value 111 and generates a control signal 121 to control the motor coils of the fan 14 to alternately work and thus to make the fan 14 rotate continuously according to the measurement value 111. The digital-to-analog converter 13 converts a pulse width modulation signal 131 into a direct current (DC) signal 132 to drive the motor coils of the fan 14 to work alternately.
In addition, referring to FIG. 1B, another conventional fan control device includes an impeller sensor 15, a digital-to-analog converter 16 and a driving chip 17. The impeller sensor 15 measures a position of an impeller of a fan 18 and generates a measurement value 151 according to the position of the impeller. The digital-to-analog converter 16 converts a pulse width modulation signal 161 into a DC signal 162. The driving chip 17 receives the measurement value 151 and the DC signal 162, and generates a driving signal 171 to drive the motor coils of the fan 18 to work alternately according to the measurement value 151 and the DC signal 162.
As shown in FIGS. 1A, 1B, 2A and 2B, the voltage value or the width ratio between the voltage pulses in the conventional pulse width modulation signal 131 (or 161) may represent a target rotation speed of the fan 14 (or 18). The voltage value of the DC signal 132 (or 162) generated by the digital-to-analog converter 13 (or 16) varies linearly according to the voltage value or the width ratio between the voltage pulses of the pulse width modulation signal 131 (or 161). Thus, the fan 14 (or 18) is driven to generate different rotation speeds. The actual rotation speed of the fan 14 (or 18) may be controlled at the target rotation speed represented by the pulse width modulation signal 131 (or 161), and the relationship between the actual rotation speed and the target rotation speed of the fan 14 (or 18) is made linear.
However, the motor of the fan 14 (or 18) may be affected by, for example, hysteresis, friction forces or inertia. Accordingly, the perfectly linear relationship L1 between the actual rotation speed and the target rotation speed of the fan 14 (or 18) does not exist. Instead, the relationship therebetween corresponds to a curve L2 concave upwards or a curve L3 concave downwards, and the actual rotation speed of the fan 14 (or 18) cannot be precisely controlled.
Therefore, it is an important subject of the invention to provide a fan control device and a fan control method for precisely controlling the actual rotation speed of the fan according to the target rotation speed of the fan and thus improving the problem caused by the nonlinear relationship between the actual rotation speed and the target rotation speed of the fan.